Personal Hydrofoil with reflexed camber line wing

ABSTRACT

The invention is a personal hydrofoil surfboard that has a wing with a reflexed mean camber line. The invention has greatly improved handling characteristics compared to hydrofoils using conventional wing designs.

CROSS-REFERENCE TO RELATED APPLICATIONS

N/A

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to personal hydrofoil watercraft used for utility or recreation. Said craft may be used in flat waters or for surfing waves or boat wakes. Said craft may be propelled, by surfing the surface of a wave or ocean swell, by towing with a kite, towed by a boat, self propelled with a motor, or human propelled using a leg pumping technique.

2. Description of Related Art

The majority of successful personal hydrofoil designs are based on the design originally described in U.S. Pat. No. 7,232,355 by Wooley. This hydrofoil design has been extensively used for personal kite powered hydrofoils as well as towing behind a boat. The most popular use is with the rider standing on a board, rather than seated as described by Wooley. The Wooley design is passively stabilized by the downward force provided by the stabilizer, in a configuration which is identical to that used in conventional aircraft. Steering and height control are achieved by weight shifts of the rider. Augera in U.S. Pat. No. 9,789,935 describes such a configuration optimized for stand up paddling in the surf Langelaan describes the use of this hydrofoil configuration in conjunction with an electrically powered immersed prop drive attached to the hydrofoil in U.S. Pat. No. 9586659 B2. Shane in U.S. Pat. No. 7,021,232 describes a human powered hydrofoil with a different configuration and stabilization method.

BRIEF SUMMARY OF THE INVENTION

The present invention is a personal hydrofoil surfboard design that has a wing with a reflexed mean camber line. This type of wing has a low negative pitching moment, zero pitching moment or even positive pitching moment. The present invention greatly improves the controllability and ease of use of the hydrofoil. The hydrofoil is much more stable than conventional designs at high speed when the angle of attack may be negative and conventional wings will suddenly develop negative lift. Moreover, the balance point does not shift forward or back as the foil is loaded and unloaded during foot transitions as it does in conventional designs. This makes it much easier to tack and jibe the hydrofoil. These attributes allow a hydrofoil of the present invention to be stable and yet highly responsive. Additionally, the low pitching moment of the reflexed wing allows the use of the hydrofoil without a stabilizer if that is desired.

To my knowledge, a reflexed airfoil has never been used in hydrofoil applications and is rarely used in aviation. It is exclusively used in tailless flying wing designs, which require pitch stability without the use of a stabilizer. Reflexed airfoils provide less lift per wing area than conventional airfoils and therefore are not used in conventional aircraft configurations. It is surprising and unexpected that. wings with reflex camber lines have a very significant benefit when used on hydrofoils, and most surprisingly that this benefit is present on hydrofoils equipped with a stabilizer.

The current invention consists of a support platform generally shaped as a surfboard. A streamlined strut is rigidly attached to the bottom of the support platform at the center line and approximately 70% of the way back from the front of the board. The strut can be detachable from the board for ease of transportation. The strut extends downward and is typically 40 to 110 cm long. A wing with a reflexed mean camber line may be attached directly to the strut, but typically, a fuselage is rigidly attached to the bottom of the strut, typically using bolt fasteners, and is aligned with and parallel to the long axis of the support platform. A one piece, strut/fuselage component may also be used. A wing with a reflexed mean camber line and providing upward lift is attached to the front of the fuselage. The wing area is typically 300 to 3000 sq cm. A stabilizer is rigidly attached at the aft of the fuselage and has an area typical between 175 and 500 sq cm. The stabilizer is set at an angle of attack less than that of the wing and provides a stabilizing down force during hydrofoil flight. The force configuration of the wing and stabilizer is that used on conventional airplane designs, where the center of mass of the airplane is in front of the center of lift of the main wing and the stabilizer provides a balancing down force. The stabilizer angle is typically 0 to −5 degrees with respect to the wing. If a lifting foil section is used for the stabilizer, this foil section will be upside down with respect to the wing, since down force is desired. A canard wing configuration could also be used and is also a subject of the current invention. In a canard configuration the stabilizer will be mounted in front of the wing and will provide up force as is typical in canard aircraft. Using a wing with a reflexed mean camber line, without a stabilizer, is also a subject of the present invention.

The airfoil of the main wing has a reflexed mean camber line which results in a pitching moment that is slightly negative, zero or even positive. The pitching moment on typical airfoils such as the SD7037 is about −0.08 at zero degrees of angle of attack (AOA). Airfoils of the current invention such as the Eppler 335 have pitching moments of −0.02 at an AOA of zero and positive pitching moments at positive AOA.

The foil sections typically used in tailless flying wing aircraft may be used. The HQ 34, NACA 24112, and Eppler 335 are typical examples. The distinguishing characteristic of a reflexed wing is that its mean camber line has an inflection point. Conventional airfoils have downward facing concave, mean camber lines. Reflexed airfoils have downward facing concave mean camber lines at the forward portion of the wing, and upward facing concave mean camber lines at the rear portion of the wing. In layman's terms the trailing edge of the wing is oriented upward rather than downward as in a conventional wing. This is illustrated in FIG. 2.

It is appreciated that a reflexed airfoil may also be used with a swept back wing with wing washout to make the pitching moment even more positive. Using swept back wings with a reflexed airfoil, which also have washout in the wing tips, is also a subject of the present invention.

The wing thickness may be between 5% to 35% of the chord. Wings with thicknesses of 8% to 18% of the chord length are preferred.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its assembly and operation may be further understood from the following description of the preferred practices thereof, which are shown by way of example in the accompanying drawings, wherein:

FIG. 1 is a side view of the present invention;

FIG. 2 is a view of a reflexed airfoil section and a comparison conventional airfoil section.

DETAILED DESCRIPTION OF THE INVENTION

Turning now in greater detail to the appended drawings, FIG. 1. FIG. 1 shows a side view of the present invention. The upper surface of support platform (1) provides a place for the rider (2) to stand, sit, or lay on. The strut (3) is detachably and rigidly affixed to the bottom of the support platform (1). The strut (3) is approximately perpendicular to the bottom of the support platform (1). The fuselage (4) is rigidly attached to the bottom of the strut (3). The strut (3) to fuselage (4) connection may be detachable for ease of transportation or may be permanent. The wing (5) has a reflexed mean camber line and is rigidly affixed to the front of the fuselage (4). This attachment may be permanent or detachable. The angle of attack of the wing (5) is approximately parallel to the long axis of the fuselage (4). The stabilizer (6) is rigidly attached to the rear of the fuselage (4). The attachment may be permanent or detachable. The angle of attack of the stabilizer (6) is negative with respect to that of the wing (5). The water surface is indicated as (7).

The current invention may also be practiced without stabilizer (6) by simply omitting it. In this case the fuselage (4) may be truncated behind the strut (3) attachment area.

The present invention is a personal hydrofoil surfboard comprised of a rigid elongated platform to support a human rider, at least one wing, at least one wing having a reflex camber line, and a connecting means between said elongated platform and said wings. Said wings are situated beneath and rigidly connected to said elongated platform via a connecting means.

In a canard configuration, a wing having a reflexed mean camber line will be rigidly attached to rear of the fuselage and will provide an upward force, and a stabilizer wing will be rigidly attached to the front of the fuselage and will provide an upward force.

Accordingly, while the preferred embodiments have been shown and described in detail by way of example, further modifications and embodiments are possible without departing from the scope of the invention. 

1. A hydrofoil surfboard that supports a human rider, comprising: a. a rigid elongated platform having a longitudinal central axis and a front end and a back end and a top surface and a bottom surface; b. at least one wing having a center axis, and a front end and back end; c. at least one of the said wings having a reflexed mean camber line; d. a connecting means; Said wing or wings being situated below said elongated platform, approximately parallel to the bottom surface of said platform. Said wing's or wings'center axis roughly aligned with the long axis of said elongated platform. Said wing's or wings' front end and back end aligned with said elongated platform's front end and back end. Said connecting means rigidly connecting the bottom surface of said platform to said wings.
 2. A hydrofoil surfboard in accordance with claim 1, comprised of: a. a rigid elongated platform having a longitudinal central axis and a front end and a back end and a top surface and a bottom surface; b. a wing with a center axis, a front end and back end, and a reflexed mean camber line; c. a stabilizer wing having a center axis, and a front end and back end; d. a fuselage having a front end and rear end and with a long axis which is aligned with the longitudinal central axis of said elongated platform; e. a streamlined strut having an upper end and a lower end, roughly vertically oriented and aligned with the longitudinal central axis of said elongated platform; The upper end of said streamlined strut being rigidly attached to the bottom surface of said elongated platform, approximately 70% back from the front end of said elongated platform and approximately perpendicular to the bottom surface of said elongated platform. Said fuselage being rigidly attached to the bottom end of said streamlined strut with its front end and rear end aligned with the front end and rear end of said elongated platform. Said wing being situated below said elongated platform, approximately parallel to the bottom surface of said platform. Said wing's center axis roughly aligned with the longitudinal central axis of said elongated platform. Said wing's front end and back end aligned with said elongated platform's front end and back end. Said wing being rigidly attached to the front end of said fuselage. Said wing providing an upward force. Said stabilizer wing being situated below said elongated platform, approximately parallel to the bottom surface of said platform. Said stabilizer wing's center axis roughly aligned with the longitudinal central axis of said elongated platform. Said stabilizer wing's front end and back end aligned with said elongated platform's front end and back end. Said stabilizer wing being rigidly attached to the rear end of said fuselage. Said stabilizer wing providing a downward force.
 3. A hydrofoil surfboard in accordance with claim 1, comprising: a. a rigid elongated platform having a longitudinal central axis and a front end and a back end and a top surface and a bottom surface; b. a wing having a center axis, a front end and back end, and a reflexed mean camber line; c. a fuselage having a front end and rear end and with a long axis which is aligned with the longitudinal central axis of said elongated platform; d. a streamlined strut having an upper end and a lower end, roughly vertically oriented and aligned with the longitudinal central axis of said elongated platform; The upper end of said streamlined strut being rigidly attached to the bottom surface of said elongated platform, approximately 70% back from the front end of said elongated platform and approximately perpendicular to the bottom surface of said elongated platform. Said fuselage being rigidly attached to the bottom end of said streamlined strut with said fuselage front end and rear end aligned with the front end and rear end of said elongated platform. Said wing being situated below said elongated platform, approximately parallel to the bottom surface of said platform. Said wing's center axis roughly aligned with the long axis of said platform. Said wing's front end and back end aligned with said elongated platform's front end and back end. Said wing being rigidly attached to the front end of said fuselage. Said wing providing an upward force.
 4. A hydrofoil surfboard in accordance with claim 1, comprised of: a. a rigid elongated platform having a longitudinal central axis and a front end and a back end and a top surface and a bottom surface; b. a wing having a center axis, a front end and back end, and a reflexed mean camber; c. a stabilizer wing having a center axis, and a front end and back end; d. a fuselage having a front end and rear end and with a long axis which is aligned with the longitudinal central axis of said elongated platform; e. a streamlined strut having an upper end and a lower end, roughly vertically oriented and aligned with the longitudinal central axis of said elongated platform; The upper end of said streamlined strut being rigidly attached to the bottom surface of said elongated platform, approximately 70% back from the front end of said elongated platform and approximately perpendicular to the bottom surface of said elongated platform. Said fuselage being rigidly attached to the bottom end of said streamlined strut with its front end and rear end aligned with the front end and rear end of said elongated platform. Said wing being situated below said elongated platform, approximately parallel to the bottom surface of said platform. Said wing's center axis roughly aligned with the long axis of said platform. Said wing's front end and back end aligned with said platform's front end and back end. Said wing being rigidly attached to the back end of said fuselage. Said wing providing an upward force. Said stabilizer wing being situated below said elongated platform, approximately parallel to the bottom surface of said platform. Said stabilizer's center axis roughly aligned with the long axis of said platform. Said stabilizer wing's front end and back end aligned with said elongated platform's front end and back end. Said stabilizer being rigidly attached to the front end of said fuselage. Said stabilizer providing an upward force. 